1. Field of the Invention
The present invention relates to a discharge plasma processing system for performing a processing operation such as etching, sputtering, coating and CVD on an object such as a substrate or a target by utilizing discharged plasma.
2. Related Background Art
Magnetic neutral line discharge or loop discharge plasma systems have been proposed in Japanese Patents Nos. 2705897 and 3177573. The effectiveness of such systems has been verified and their industrial merits have been acknowledged. The magnetic neutral line discharge or loop discharge (also referred to as NLD for abbreviation) plasma has two major features that other plasma systems do not have.
One of the features is that it provides time/space controllability relative to the size and the location of plasma to be generated. In other words, both the size and the location of required plasma can be changed in terms of both time and space. This is because a magnetic neutral line in a vacuum chamber can be formed by outside control without difficulty and plasma can be generated along the profile of the magnetic neutral line. This type of freedom is not found in any other systems.
The other feature is that the NLD plasma does not contain higher temperature component which is not necessary for surface treatments and a higher density plasma can be produced under a lower gas pressure supply, comparing with any other plasma production method.
These features come from so-called a chaotic phenomenon of electrons generated and located around a magnetic neutral line due to meandering motions crossing the neutral line when an rf electric field is applied to the neutral line.
Electrons to be generated around the neutral line are well heated and thermalized so chaotically that result in rise up of electron density itself rather than increase of temperature under ordinary rf electric field application
Higher density electrons of lower temperature make easier transfer of electron energy to neutrals and ions so that a lower temperature and higher density plasma can be generated under lower pressure gas supply. This leads us such plasma is useful for damage-less and high through put operation of surface processing. Actually, the NLD system: magnetic neutral line discharge plasma processing systems are performing remarkably well in the field of ultra-micro processing that increasingly requires high processing precision such as glass processing for micro-lenses and optical wave-guides and etching of low dielectric materials.
FIG. 1 of the accompanying drawings is a conceptual illustration of a magnetic neutral line discharge plasma processing system manufactured for the purpose of processing the surface of a disk-shaped substrate. Such systems have been manufactured to date. Referring to FIG. 1, the illustrated system comprises a cylindrical vacuum chamber A, and three coils including an upper coil B, a middle coil C and a lower coil D that are arranged coaxially outside the vacuum chamber A. A circular magnetic neutral line E is produced in the cylindrical vacuum chamber A by regulating currents made to flow to the three coils B, C and D. Plasma is generated in the form of a doughnut having a core of circular magnetic neutral line E by an induction field directed to the azimuth that is generated by an excitation current flowing to RF coil G wound outside an insulating cylindrical vacuum wall F typically made of ceramic. For this process, the diameter and the vertical position of the doughnut-like plasma can be freely controlled by the combination of the electric currents made to flow to the coils B, C and D even during the processing operation.
As pointed out above, high density and low temperature plasma is generated by using low pressure gas in a magnetic neutral line discharge plasma processing system and this feature is very advantageous when it is exploited for various processing operations. Thus, there is a strong demand for improved magnetic neutral line discharge plasma processing systems that have characteristic features that are not found in any other type systems.
While the magnetic neutral line discharge plasma processing systems perform remarkably well as described above, they still have room for improvement from the viewpoint of ease of handling and reduction of the period necessary for servicing and adjustment. Additionally, the system itself can be expensive particularly when costly ceramic is used for the purpose of acquiring desired properties including toughness and resistance against vacuum. Therefore, development of less costly novel materials that will be commercially available has been eagerly waited for.
In the case of currently available circular magnetic neutral line discharge plasma, theoretically a cylindrical ceramic container has to be used as lateral wall of a vacuum chamber and one-turn coil for a radio frequency (RF) has to be wound around the outer periphery of the container in order to apply an electric field along a circular magnetic neutral line. However, a thick-walled cylindrical ceramic container having a diameter of tens of several centimeters is expensive and, if the inner wall surface that is located at the vacuum side is made very smooth, some measures need to be taken to eliminate or prevent adsorption attributable to affinity for gas of a special type. As pointed out above, the use of costly ceramic as wall material for the purpose of acquiring desired properties including toughness and resistance against vacuum raises the cost of the system itself particularly when the system is large. This is also a problem to be dissolved for processing operations using ICP, type processing systems.
Therefore, the present invention needs to dissolve the above identified problems.
Additionally, conventional three magnetic field coil type processing systems as illustrated in FIG. 1 are required to be lightweight and energy saving and, at the same time, have a reduced number of components that is to be achieved by reducing the number of coils as many as possible from the viewpoint of arrangement of other components for plasma processing.